Electrical connectors are used in many electronic systems. It is generally easier and more cost effective to manufacture a system on several printed circuit boards that are then joined together with electrical connectors. A traditional arrangement for joining several printed circuit boards is to have one printed circuit board serve as a backplane. Other printed circuit boards, called daughter boards, are connected through the backplane.
A traditional backplane is a printed circuit board with many connectors. Conducting traces in the printed circuit board connect to signal pins in the connectors so signals may be routed between the connectors. Daughter boards also contain connectors that are plugged into the connectors on the backplane. In this way, signals are routed among the daughter boards through the backplane. The daughter cards often plug into the backplane a. a right angle. The connectors used for these applications contain a right angle bend and are often called xe2x80x9cright angle connectors.xe2x80x9d
Connectors are also used in other configurations for interconnecting printed circuit boards, and even for connecting cables to printed circuit boards. Sometimes, one or more small printed circuit boards are connected to another larger printed circuit board. The larger printed circuit board is called a xe2x80x9cmother boardxe2x80x9d and the printed circuit boards plugged into it are called daughter boards. Also, boards of the same size are sometimes aligned in parallel. Connectors used in these applications are sometimes called xe2x80x9cstacking connectorsxe2x80x9d or xe2x80x9cmezzanine connectors.xe2x80x9d
Regardless of the exact application, electrical connector designs have generally needed to mirror trends in the electronics industry. Electronic systems generally have gotten smaller and faster. They also handle much more data than systems built just a few years ago. These trends mean that electrical connectors must carry more and faster data signals in a smaller space without degrading the signal.
Connectors can be made to carry more signals in less space by placing the signal contacts in the connector closer together. Such connectors are called xe2x80x9chigh density connectors.xe2x80x9d The difficulty with placing signal contacts closer together is that there is electromagnetic coupling between the signal contacts. As the signal contacts are placed closer together, the electromagnetic coupling increases. Electromagnetic coupling also increases as the speed of the signals increase.
In a conductor, electromagnetic coupling is indicated by measuring the xe2x80x9ccross talkxe2x80x9d of the connector. Cross talk is generally measured by placing a signal on one or more signal contacts and measuring the amount of signal coupled to another signal contact. The choice of which signal contacts are used for the cross talk measurement as well as the connections to the other signal contacts will influence the numerical value of the cross talk measurement. However, any reliable measure of cross talk should show that the cross talk increases as the speed of the signals increases and also as the signal contacts are placed closer together.
A traditional method of reducing cross talk is to ground signal pins within the field of the signal pins. The disadvantage of this approach is that it reduces the effective signal density of the connector.
To make both a high speed and high density connector, connector designers have inserted shield members between signal contacts. The shields reduce the electromagnetic coupling between signal contacts, thus countering the effect of closer spacing or higher frequency signals. Shielding, if appropriately configured, can also control the impedance of the signal paths through the connector, which can also improve the integrity of signals carried by the connector.
An early use of shielding is shown in Japanese patent disclosure 49-6543 by Fujitsu, Ltd. dated Feb. 15, 1974. U.S. Pat. Nos. 4,632,476 and 4,806,107, both assigned to ATandT Bell Laboratories, show connector designs in which shields are used between columns of signal contacts. These patents describe connectors in which the shields run parallel to the signal contacts through both the daughter board and the backplane connectors. Cantilevered beams are used to make electrical contact between the shield and the backplane connectors. U.S. Pat. Nos. 5,433,617; 5,429,521; 5,429,520 and 5,433,618, all assigned to Framatome Connectors International, show a similar arrangement. The electrical connection between the backplane and shield is, however, made with a spring type contact.
Other connectors have the shield plate within only the daughter card connector. Examples of such connector designs can be found in U.S. Pat. Nos. 4,846,727, 4,975,084, 5,496,183 and 5,066,236, all assigned to AMP, Inc. Another connector with shields only within the daughter board connector is shown in U.S. Pat. No. 5,484,310, assigned to Teradyne, Inc.
In patent application Ser. No. 09/156,227, assigned to Teradyne, Inc. and which is hereby incorporated by reference, a circuit board connector is shown. The connector is formed from two identical halves. Each half includes an insulative housing, a ground insert and a column of signal contacts. The two halves are mounted to opposite sides of a first printed circuit board. The plurality of signal contacts extend from a first surface of the housing and are attached to the first circuit board. The signal contacts extend through the insulative housing, extending from a second surface of the housing, and are bent to form spring contacts. The connector may then be mounted to a second circuit board by pressing the spring contacts into signal contact pads on the second circuit board, thus completing signal paths between the first and second circuit boards.
A modular approach to connector systems was introduced by Teradyne Connection Systems, of Nashua, New Hampshire. In a connector system called HD+(copyright), multiple modules or columns of signal contacts are arranged on a metal stiffener. Typically, 15 to 20 such columns are provided in each module. A more flexible configuration results from the modularity of the connector such that connectors xe2x80x9ccustomizedxe2x80x9d for a particular application do not require specialized tooling or machinery to create. In addition, many tolerance issues that occur in larger non-modular connectors may be avoided.
A more recent development in such modular connectors was introduced by Teradyne, Inc. and is shown in U.S. Pat. Nos. 5,980,321 and 5,993,259 which are hereby incorporated by reference. Teradyne, Inc., assignee of the above-identified patents, sells a commercial embodiment under the trade name VHDM(trademark).
The patents show a two piece connector. A daughter card portion of the connector includes a plurality of modules held on a metal stiffener. Here, each module is assembled from two wafers, a ground wafer and a signal wafer. The backplane connector, or pin header, includes columns of signal pins with a plurality of backplane shields located between adjacent columns of signal pins.
Yet another variation of a modular connector is disclosed in U.S. patent application Ser. No. 09/199,126 which is hereby incorporated by reference. Teradyne Inc., assignee of the patent application, sells a commercial embodiment of the connector under the trade name VHDMxe2x80x94HSD. The application shows a connector similar to the VHDM(trademark) connector, a modular connector held together on a metal stiffener, each module being assembled from two wafers. The wafers shown in the patent application, however, have signal contacts arranged in pairs. These contact pairs are configured to provide a differential signal. Signal contacts that comprise a pair are spaced closer to each other than either contact is to an adjacent signal contact that is a member of a different signal pair.
As described in the background, higher speed and higher density connectors are required to keep pace with the trends in the electronic systems industry. Constraints imposed by the geometries of backplanes designed for certain applications however, reduce the options available for possible connector solutions.
For example, thick, large backplanes make some surface mount connectors impractical as the number-of layers in the board hinders raising the board to a temperature necessary to solder the leads to the board. Press fit connectors require larger vias. As via diameters increase, the capacitance of the via also increases thus making an impedance match between the connector and the characteristic impedance of a transmission line on the backplane more difficult. In addition, larger vias consume more real estate on the backplane which, in the alternative, could be used to route wider signal traces which can be used to control conductive losses.
One connector solution described in the following disclosure provides a high speed, high density pressure mounted connector. The connector is comprised of a plurality of wafers suspended from a member which provides an organized presentation of the wafers. In an illustrated embodiment, the member is shown as a metal stiffener.
In a preferred embodiment, the wafers are comprised of two halves, a first half including both signal and ground conductors and a second including only signal conductors. When attached, the two halves form a single wafer in which signal conductors are arranged in pairs which, in a preferred embodiment, are configured to provide a differential signal. A ground conductor is provided proximate to the differential signal pair. The conductor tails are configured at a first end as pressure mount contacts to make contact with signal and ground launches located on a surface of a backplane. With such an arrangement, the signal and ground launches on the backplane may be used with smaller diameter vias.